Fatigue in road traffic is one of the main causes of accidents. Driver assistance systems (DAS) offer the opportunity of automatically detecting driver fatigue and of warning the driver in case of an unfitness to drive.
For this purpose driver assistance systems include a fatigue detection system. The latter is defined here as a system located within the vehicle, which monitors the driver behavior and is activated if the driver appears to be impaired due to fatigue. The main objective is to prevent a micro sleep event while operating a car.
Scaling methods based on monitoring make it possible to allocate the fatigue of the vehicle driver to a specific fatigue degree. The use of standardized scales ensures the most objective fatigue estimate possible. Two of the most common scales were established by Wierwille and Ellsworth (abbreviated: Wierwille scale) and with Human Factors Consult GmbH Berlin (abbreviated: HFC scale). The Wierville scale includes four stages of driver fatigue, which range from 1=not fatigued, to 4=extremely fatigued. Each stage is characterized by specific eye parameters and behavior indicators. The HFC scale includes nine stages of fatigue, which range from 1=awake to 9=sleep. Nine indicators are used for classifying a driver state. Another scaling possibility is offered by the TU-Berlin drowsiness scale (abbreviated: TUBS scale).
Previous systems for fatigue detection now use prediction algorithms to calculate the fatigue degree on the basis of sensor data. Such a sensor-based fatigue detection in real time may take into account the available driving performance parameters (steering motions, speed, lane keeping) or characteristic data of the vehicle driver, such as the eye movement or blinking behavior, the head position and head movement, the heart rate or similar biophysical parameters.
However, the customer using the driver assistance systems currently on the market finds it difficult to notice or actually experience detected fatigue. The reason for this is that the fatigue detection invariably becomes noticeable only after a predefined fatigue degree has been reached. This may be due to the circumstance that the conventional fatigue detection systems supply only a value for the current fatigue state of the driver.